Drugs binding to a recognition sites for endogenous ligands can act as agonists and antagonists. An imidazobenzodiazepinone derivative, Ro 151788 is the first representative of specific benzodiazepine antagonists. However since anxiolytic benzodiazepines probably act as antagonists the RO 151788 may be acting as an agonist, that is it mimics the endogenous agonist. Studies with isoniazid show that benzodiazepines antagonize the convulsant action of isoniazid doses that deplete brain GABA by about 50%, in contrast RO 151788 facilitate these convulsions.